One objective of orthodontics is to move a patient's teeth to positions where the teeth function optimally and are also aesthetically pleasing. Conventional appliances such as braces and wires are applied to the teeth of a patient by an orthodontist. Once mounted on the teeth, the braces exert continual force on the teeth and gradually urge the teeth to their respective ideal position. The orthodontist does this by adjusting the wires over time to move the teeth toward their final destination.
Orthodontic brackets are often bonded directly to the patient's teeth. Typically, a small quantity of adhesive is placed on the base of each bracket and the bracket is then placed on a selected tooth. Before the adhesive is set, the bracket is maneuvered to a desired location on the tooth. Once the adhesive has hardened, the bracket is bonded to the tooth with sufficient strength to withstand subsequent orthodontic forces as treatment progresses. One shortcoming with this technique is the difficulty in accessing the optimal surface for bracket placement on severely crowded teeth or in teeth where the bonding surface is obstructed by teeth in the opposing arch during jaw closure. With posterior teeth, the treatment provider may have difficulty seeing the precise position of the bracket relative to the tooth surface. The amount of time needed to carry out the bonding procedure may be a nuisance both to the patient as well as to the treatment provider. Also, the necessity of minimizing moisture contamination from the patient's saliva can prolong the procedure and also unduly impair the accuracy of placement of the brackets on the teeth. All of these factors increase the chance that one or more brackets will be incorrectly positioned on the teeth.
Apparatus, systems, and methods have been developed to facilitate teeth movement utilizing clear, removable teeth aligners as an alternative to braces. A system that utilizes multiple, removable aligners is described in U.S. Pat. No. 5,975,893, assigned to the same assignee as this application. A mold of the patient's bite is initially taken and desired ending positions for the patient's teeth (i.e., a functionally and/or aesthetically optimum position) are determined, based on a prescription provided by an orthodontist or dentist. Corrective paths between the initial positions of the teeth and their desired ending positions are then planned. These corrective paths generally include a plurality of intermediate positions between the initial and ending positions of the teeth. Multiple clear, removable aligners formed to move the teeth to the various positions along the corrective path are then manufactured. One system for providing such aligners is the Invisalign® System from Align Technologies, Inc. of Santa Clara, Calif.
The planning of the corrective paths for the teeth often involves various orthodontic measurements and diagnostics. Many of these measurements utilize a mathematical model of the tooth, including portions of the tooth that are not visible to the naked eye such as its root. Currently, the tooth's axes are constructed manually such that the tooth's model, including its root may be constructed. However, this is a tedious, time consuming process that is subject to human error. Automatic construction of the tooth's axes is desirable as it would save time and eliminate human error.